ALEC · Alector, Inc.

The reported shares are represented by restricted stock units, or RSUs, which vest in 12 equal quarterly installments beginning on September 1, 2026.

The shares subject to the option vest in 12 equal monthly installments beginning on July 17, 2026, provided that the shares subject to the option will vest in full on the earlier of the one-year anniversary of the date of grant or the date of the Issuer's next annual meeting of stockholders.

The shares subject to the option vest in 12 equal monthly installments beginning on July 17, 2026, provided that the shares subject to the option will vest in full on the earlier of the one-year anniversary of the date of grant or the date of the Issuer's next annual meeting of stockholders.

The reported shares are represented by restricted stock units, or RSUs, which vest on the earlier of (i) June 17, 2027 or (ii) the date of the Issuer's next annual meeting of stockholders.

The shares subject to the option vest in 12 equal monthly installments beginning on July 17, 2026, provided that the shares subject to the option will vest in full on the earlier of the one-year anniversary of the date of grant or the date of the Issuer's next annual meeting of stockholders.

The reported shares are represented by restricted stock units, or RSUs, which vest on the earlier of (i) June 17, 2027 or (ii) the date of the Issuer's next annual meeting of stockholders.

The reported shares are represented by restricted stock units, or RSUs, which vest on the earlier of (i) June 17, 2027 or (ii) the date of the Issuer's next annual meeting of stockholders.

The reported shares are represented by restricted stock units, or RSUs, which vest on the earlier of (i) June 16, 2027 or (ii) the date of the Issuer's next annual meeting of stockholders.

The reported shares are represented by restricted stock units, or RSUs, which vest on the earlier of (i) June 17, 2027 or (ii) the date of the Issuer's next annual meeting of stockholders.

The shares subject to the option vest in 12 equal monthly installments beginning on July 17, 2026, provided that the shares subject to the option will vest in full on the earlier of the one-year anniversary of the date of grant or the date of the Issuer's next annual meeting of stockholders.

The shares subject to the option vest in 12 equal monthly installments beginning on July 17, 2026, provided that the shares subject to the option will vest in full on the earlier of the one-year anniversary of the date of grant or the date of the Issuer's next annual meeting of stockholders.

The reported shares are represented by restricted stock units, or RSUs, which vest on the earlier of (i) June 17, 2027 or (ii) the date of the Issuer's next annual meeting of stockholders.

The shares subject to the option vest in 12 equal monthly installments beginning on July 17, 2026, provided that the shares subject to the option will vest in full on the earlier of the one-year anniversary of the date of grant or the date of the Issuer's next annual meeting of stockholders.

The reported shares are represented by restricted stock units, or RSUs, which vest on the earlier of (i) June 17, 2027 or (ii) the date of the Issuer's next annual meeting of stockholders.

The shares subject to the option vest in 12 equal monthly installments beginning on July 17, 2026, provided that the shares subject to the option will vest in full on the earlier of the one-year anniversary of the date of grant or the date of the Issuer's next annual meeting of stockholders.

The sales reported in this Form 4 were effected pursuant to a Rule 10b5-1 Trading Plan adopted by the reporting person on September 5, 2025.

The price reported in Column 4 is a weighted average price. The shares were sold in multiple transactions at prices ranging from $1.86 to $1.94. Full information regarding the number of shares sold at each separate price can be furnished to the SEC staff, the issuer, or any security holder of the issuer upon request.

The reported shares were sold to satisfy the reporting person's tax obligations in connection with the vesting of restricted stock units, or RSUs.

The price reported in Column 4 is a weighted average price. The shares were sold in multiple transactions at prices ranging from $1.92 to $2.08. Full information regarding the number of shares sold at each separate price can be furnished to the SEC staff, the issuer, or any security holder of the issuer upon request.

The reported shares were sold to satisfy the reporting person's tax obligations in connection with the vesting of restricted stock units, or RSUs.

The price reported in Column 4 is a weighted average price. The shares were sold in multiple transactions at prices ranging from $1.92 to $2.08. Full information regarding the number of shares sold at each separate price can be furnished to the SEC staff, the issuer, or any security holder of the issuer upon request.

The reported shares were sold to satisfy the reporting person's tax obligations in connection with the vesting of restricted stock units, or RSUs.

The price reported in Column 4 is a weighted average price. The shares were sold in multiple transactions at prices ranging from $1.92 to $2.08. Full information regarding the number of shares sold at each separate price can be furnished to the SEC staff, the issuer, or any security holder of the issuer upon request.

The reported shares are represented by restricted stock units, or RSUs, which vest in 4 equal quarterly installments beginning on June 1, 2026.

The sales reported in this Form 4 were effected pursuant to a Rule 10b5-1 Trading Plan adopted by the reporting person on September 5, 2025.

The reported shares are represented by restricted stock units, or RSUs, one half (1/2) of the total shares shall vest on September 1, 2026 and one half (1/2th) of the total shares shall vest on March 1, 2027.

The reported shares are represented by restricted stock units, or RSUs, one half (1/2) of the total shares shall vest on September 1, 2026 and one half (1/2th) of the total shares shall vest on March 1, 2027.

The sales reported in this Form 4 were effected pursuant to a Rule 10b5-1 Trading Plan adopted by the reporting person on September 5, 2025.

The sales reported in this Form 4 were effected pursuant to a Rule 10b5-1 Trading Plan adopted by the reporting person on September 5, 2025.

The price reported in Column 4 is a weighted average price. The shares were sold in multiple transactions at prices ranging from $2.06 to $2.12. Full information regarding the number of shares sold at each separate price can be furnished to the SEC staff, the issuer, or any security holder of the issuer upon request.

The reported shares were sold to satisfy the reporting person's tax obligations in connection with the vesting of restricted stock units, or RSUs.

The price reported in Column 4 is a weighted average price. The shares were sold in multiple transactions at prices ranging from $2.04 to $2.37. Full information regarding the number of shares sold at each separate price can be furnished to the SEC staff, the issuer, or any security holder of the issuer upon request.

The reported shares were sold to satisfy the reporting person's tax obligations in connection with the vesting of restricted stock units, or RSUs.

The price reported in Column 4 is a weighted average price. The shares were sold in multiple transactions at prices ranging from $2.04 to $2.37. Full information regarding the number of shares sold at each separate price can be furnished to the SEC staff, the issuer, or any security holder of the issuer upon request.

The reported shares were sold to satisfy the reporting person's tax obligations in connection with the vesting of restricted stock units, or RSUs.

The price reported in Column 4 is a weighted average price. The shares were sold in multiple transactions at prices ranging from $2.04 to $2.37. Full information regarding the number of shares sold at each separate price can be furnished to the SEC staff, the issuer, or any security holder of the issuer upon request.

The sales reported in this Form 4 were effected pursuant to a Rule 10b5-1 Trading Plan adopted by the reporting person on September 5, 2025.

The sale reported in this Form 4 was effected pursuant to a Rule 10b5-1 trading plan adopted by the reporting person on September 5, 2025.

The reported shares were sold to satisfy the reporting person's tax obligations in connection with the vesting of restricted stock units, or RSUs.

The price reported in Column 4 is a weighted average price. The shares were sold in multiple transactions at prices ranging from $1.095 to $1.14. Full information regarding the number of shares sold at each separate price can be furnished to the SEC staff, the issuer, or any security holder of the issuer upon request.

The reported shares were sold to satisfy the reporting person's tax obligations in connection with the vesting of restricted stock units, or RSUs.

The price reported in Column 4 is a weighted average price. The shares were sold in multiple transactions at prices ranging from $1.095 to $1.14. Full information regarding the number of shares sold at each separate price can be furnished to the SEC staff, the issuer, or any security holder of the issuer upon request.

The reported shares were sold to satisfy the reporting person's tax obligations in connection with the vesting of restricted stock units, or RSUs.

The price reported in Column 4 is a weighted average price. The shares were sold in multiple transactions at prices ranging from $1.095 to $1.14. Full information regarding the number of shares sold at each separate price can be furnished to the SEC staff, the issuer, or any security holder of the issuer upon request.

The reported shares were sold to satisfy the reporting person's tax obligations in connection with the vesting of restricted stock units, or RSUs.

The price reported in Column 4 is a weighted average price. The shares were sold in multiple transactions at prices ranging from $1.095 to $1.14. Full information regarding the number of shares sold at each separate price can be furnished to the SEC staff, the issuer, or any security holder of the issuer upon request.

The reported shares are represented by restricted stock units, or RSUs, which vest in 12 equal quarterly installments beginning on December 1, 2025.

Shares subject to the option vest in 48 equal monthly installments beginning on December 10, 2025.

Shares subject to the option vest in 48 equal monthly installments beginning on December 10, 2025.

The reported shares are represented by restricted stock units, or RSUs, which vest in 12 equal quarterly installments beginning on December 1, 2025.

Shares subject to the option vest in 48 equal monthly installments beginning on December 10, 2025.

The reported shares are represented by restricted stock units, or RSUs, which vest in 12 equal quarterly installments beginning on December 1, 2025.

The reported shares were sold to satisfy the reporting person's tax obligations in connection with the vesting of restricted stock units, or RSUs.

The price reported in Column 4 is a weighted average price. The shares were sold in multiple transactions at prices ranging from $2.30 to $2.59. Full information regarding the number of shares sold at each separate price can be furnished to the SEC staff, the issuer, or any security holder of the issuer upon request.

The reported shares were sold to satisfy the reporting person's tax obligations in connection with the vesting of restricted stock units, or RSUs.

The price reported in Column 4 is a weighted average price. The shares were sold in multiple transactions at prices ranging from $2.30 to $2.59. Full information regarding the number of shares sold at each separate price can be furnished to the SEC staff, the issuer, or any security holder of the issuer upon request.

The reported shares were sold to satisfy the reporting person's tax obligations in connection with the vesting of restricted stock units, or RSUs.

The price reported in Column 4 is a weighted average price. The shares were sold in multiple transactions at prices ranging from $2.30 to $2.59. Full information regarding the number of shares sold at each separate price can be furnished to the SEC staff, the issuer, or any security holder of the issuer upon request.

The reported amount excludes 150,000 shares previously reported as performance share units, or PSUs. Because the performance metrics were not attained during the PSU measurement period, these PSUs were forfeited on May 6, 2025.

The reported shares were sold to satisfy the reporting person's tax obligations in connection with the vesting of restricted stock units, or RSUs.

The price reported in Column 4 is a weighted average price. The shares were sold in multiple transactions at prices ranging from $2.30 to $2.59. Full information regarding the number of shares sold at each separate price can be furnished to the SEC staff, the issuer, or any security holder of the issuer upon request.

The sales reported in this Form 4 were effected pursuant to a Rule 10b5-1 Trading Plan adopted by the reporting person on May 27, 2025.

The price reported in Column 4 is a weighted average price. The shares were sold in multiple transactions at prices ranging from $2.31 to $2.385. Full information regarding the number of shares sold at each separate price can be furnished to the SEC staff, the issuer, or any security holder of the issuer upon request.

One third (1/3rd) of the total shares subject to the option shall vest on November 1, 2025, and one twelfth (1/12th) of the total shares subject to the option shall vest in equal monthly installments thereafter, provided that the shares subject to the option will vest in full on July 1, 2026.

One third (1/3rd) of the total shares subject to the option shall vest on November 1, 2025, and one twelfth (1/12th) of the total shares subject to the option shall vest in equal monthly installments thereafter, provided that the shares subject to the option will vest in full on July 1, 2026.

The reported shares are represented by restricted stock units, or RSUs, one half (1/2) of the total shares shall vest on December 1, 2025 and one fourth (1/4th) of the total shares shall vest quarterly thereafter.

One third (1/3rd) of the total shares subject to the option shall vest on November 1, 2025, and one twelfth (1/12th) of the total shares subject to the option shall vest in equal monthly installments thereafter, provided that the shares subject to the option will vest in full on July 1, 2026.

The reported shares are represented by restricted stock units, or RSUs, one half (1/2) of the total shares shall vest on December 1, 2025 and one fourth (1/4th) of the total shares shall vest quarterly thereafter.